/*
 * Astra Utils (CRC-8)
 * http://cesbo.com/astra
 *
 * Copyright (C) 2015-2016, Artem Kharitonov <artem@3phase.pw>
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

#include <astra.h>
#include <utils/crc8.h>

/*
 * CRC-8 calculation routine as per ETSI EN 302 755.
 *
 * Polynomial used: x^8 + x^7 + x^6 + x^4 + x^2 + 1 (0xD5)
 */
static const uint8_t crc8_table[256] = {
    0x00, 0xd5, 0x7f, 0xaa, 0xfe, 0x2b, 0x81, 0x54, 0x29, 0xfc, 0x56, 0x83,
    0xd7, 0x02, 0xa8, 0x7d, 0x52, 0x87, 0x2d, 0xf8, 0xac, 0x79, 0xd3, 0x06,
    0x7b, 0xae, 0x04, 0xd1, 0x85, 0x50, 0xfa, 0x2f, 0xa4, 0x71, 0xdb, 0x0e,
    0x5a, 0x8f, 0x25, 0xf0, 0x8d, 0x58, 0xf2, 0x27, 0x73, 0xa6, 0x0c, 0xd9,
    0xf6, 0x23, 0x89, 0x5c, 0x08, 0xdd, 0x77, 0xa2, 0xdf, 0x0a, 0xa0, 0x75,
    0x21, 0xf4, 0x5e, 0x8b, 0x9d, 0x48, 0xe2, 0x37, 0x63, 0xb6, 0x1c, 0xc9,
    0xb4, 0x61, 0xcb, 0x1e, 0x4a, 0x9f, 0x35, 0xe0, 0xcf, 0x1a, 0xb0, 0x65,
    0x31, 0xe4, 0x4e, 0x9b, 0xe6, 0x33, 0x99, 0x4c, 0x18, 0xcd, 0x67, 0xb2,
    0x39, 0xec, 0x46, 0x93, 0xc7, 0x12, 0xb8, 0x6d, 0x10, 0xc5, 0x6f, 0xba,
    0xee, 0x3b, 0x91, 0x44, 0x6b, 0xbe, 0x14, 0xc1, 0x95, 0x40, 0xea, 0x3f,
    0x42, 0x97, 0x3d, 0xe8, 0xbc, 0x69, 0xc3, 0x16, 0xef, 0x3a, 0x90, 0x45,
    0x11, 0xc4, 0x6e, 0xbb, 0xc6, 0x13, 0xb9, 0x6c, 0x38, 0xed, 0x47, 0x92,
    0xbd, 0x68, 0xc2, 0x17, 0x43, 0x96, 0x3c, 0xe9, 0x94, 0x41, 0xeb, 0x3e,
    0x6a, 0xbf, 0x15, 0xc0, 0x4b, 0x9e, 0x34, 0xe1, 0xb5, 0x60, 0xca, 0x1f,
    0x62, 0xb7, 0x1d, 0xc8, 0x9c, 0x49, 0xe3, 0x36, 0x19, 0xcc, 0x66, 0xb3,
    0xe7, 0x32, 0x98, 0x4d, 0x30, 0xe5, 0x4f, 0x9a, 0xce, 0x1b, 0xb1, 0x64,
    0x72, 0xa7, 0x0d, 0xd8, 0x8c, 0x59, 0xf3, 0x26, 0x5b, 0x8e, 0x24, 0xf1,
    0xa5, 0x70, 0xda, 0x0f, 0x20, 0xf5, 0x5f, 0x8a, 0xde, 0x0b, 0xa1, 0x74,
    0x09, 0xdc, 0x76, 0xa3, 0xf7, 0x22, 0x88, 0x5d, 0xd6, 0x03, 0xa9, 0x7c,
    0x28, 0xfd, 0x57, 0x82, 0xff, 0x2a, 0x80, 0x55, 0x01, 0xd4, 0x7e, 0xab,
    0x84, 0x51, 0xfb, 0x2e, 0x7a, 0xaf, 0x05, 0xd0, 0xad, 0x78, 0xd2, 0x07,
    0x53, 0x86, 0x2c, 0xf9
};

uint8_t au_crc8(const uint8_t *buffer, size_t len)
{
    unsigned int crc = 0;

    while (len--)
    {
        const unsigned int i = (crc ^ *buffer++) & 0xFF;
        crc = (crc8_table[i] ^ (crc << 8)) & 0xFF;
    }

    return crc & 0xFF;
}
